1. Field of the Invention
The present invention relates generally to the field of voltage regulators and other high voltage equipment, and more particularly, to a method and structure for diagnosing the wear characteristic and other important characteristics of electrodes within voltage regulator/high voltage equipment.
2. Description of the Related Art
A power line voltage regulator is an electrical device which acts to effect changes in the voltage in an electrical power distribution system in response to changes in electrical load upon the power distribution system. Typically, these voltage regulators switch power at levels of approximately several hundred amperes and over ten thousand volts. The adjustment or change in the voltage is by means of a mechanism that mechanically changes the voltage by moving between a series of electrode taps (hence it is called a xe2x80x9cload tap changerxe2x80x9d, or LTC). Typically, the electrode changing mechanism will comprise a plurality of shelves which are connected into different portions of a transformer winding, so that a connection to each of the different shelves will yield a different voltage from the transformer. A tap-change electrode will be disposed on an arm and will be moved mechanically among the various shelves to a shelf with the desired voltage. In a preferred embodiment, the shelves will be disposed in a circular configuration, with an arm rotating about the center of the circle of shelves, with the arm containing at the end thereof a tap-change electrode.
Tap-changes are typically made in a voltage regulator about fifteen times per day. The tap-change electrode contacts and contacting surface (the shelf) wear out over time and need replacement. Presently, scheduled maintenance replacement of the electrodes and the shelves are made at regular intervals or after a certain number of electrode changes have been logged by a counter actuated by a micro-switch. However, not all transformers or their taps are used equally, nor are transformers always equally loaded. Hence, all LTC contacts do not age at the same rate. Differences in alignment of the shelves and other manufacturing variations may also contribute to premature degradation of the taps or of the shelves. Accordingly, a maintenance schedule based on time elapsed, or based on the number of electrode changes may result in unnecessary equipment changes or unexpected failures. Furthermore, errors are often introduced during maintenance, which results in subsequent down time. Eliminating unnecessary maintenance and performing necessary maintenance only where required will save significant resources and money.
In one embodiment, the present invention comprises a diagnostic method for determining a characteristic of electrode contacts and/or contacted surfaces including the steps of: sensing, during a movement that causes an electrode to have a break contact event with a first contacted surface and to have a make contact event with a second contacted surface, an RF signal from at least one electrical discharge event during said movement; using a parameter of the RF signal to diagnose the characteristic of the electrode contacts and/or contacted surfaces.
In a further aspect of the present invention, the using step comprises the step of determining RF activity using the break contact and make contact events and determining a delay between the break contact event and the make contact event. The using step may further comprise comparing the determined delay with a reference delay.
In a further aspect of the present invention, the using step may comprise the step of determining an amplitude of the RF signal during at least one of the break contact event and the make contact event.
In yet a further aspect of the present invention, the delay determining step may comprise the step of counting clock pulses occurring between the break contact event and the make contact event.
In yet a further aspect of the present invention, the using step may comprise the step of integrating a portion of the RF signal.
In a further aspect of the present invention, the step may be included of sensing, simultaneously with the RF signal sensing step, a vibration signal generated by at least one of the break contact event and the make contact event; and using a parameter of the vibration signal to assist in diagnosing the characteristic.
In a further aspect of the present invention, the vibration signal parameter using step may comprise the step of digitally sampling the vibration signal.
In a yet further aspect of the present invention, the parameter using steps may comprise the steps of: determining a first time when a level of activity in the vibration signal exceeds a predetermined threshold level of activity; and monitoring a parameter of the RF signal in a time period that includes the first time.
In a yet further aspect of the present invention, the parameter using steps may comprise the steps of: determining a first time and a second time when a level of activity in the vibration signal exceeds a predetermined level of activity; and monitoring a parameter of the RF signal in a time period that includes the first and second times.
In a further aspect of the present invention, the activity in said vibration signal may comprise a vibration signal amplitude.
In yet a further aspect of the present invention, the activity in said vibration signal may comprise a peak grouping above a predetermined threshold.
In a further aspect of the invention, the activity in the vibration signal may comprise an integrated signal magnitude in a predetermined time interval.
In yet a further aspect of the present invention the RF signal monitoring step may comprise the step of either monitoring the amplitude of the RF signal, or the peak groupings of the RF signal, or the integrated signal magnitude in a predetermined time interval.
In yet a further aspect of the present invention, the step is included of sending the RF signal and the vibration signal to a computing device; determining a first time and a second time when a level of activity in the vibration signal exceeds a predetermined level of activity; and measuring parameters in each of the RF signal and the vibration signal that occur during a time period that includes the first and second times; and determining the characteristic based on at least one of the measured parameters.
In a further aspect of the present invention, the using step may comprise the step of recording waveforms representing aspects of the RF signal and the simultaneously sensed vibration signal in time synchronization. By way of example, these signals could be displayed together for visual inspection.
In a further aspect of the invention, a method is provided for determining a characteristic of electrode contacts and/or contacted surfaces in a voltage regulator comprising the steps of: sensing a vibration signal from said voltage regulator; sensing simultaneously an RF signal from the voltage regulator; determining at least a first time when a level of activity in the vibration signal exceeds a predetermined threshold level of activity; measuring a first parameter of the RF signal occurring in a time period that includes the first time; measuring a second parameter of the vibration signal occurring in the time period; and determining the characteristic based on at least one of the first and second parameters.
In a further aspect of the present invention, the first parameter of the RF signal is measured substantially only around the first and second times.
In a further aspect of the present invention, the at least one of the first and second parameters is a delay measurement between the first and second times; and wherein the delay measurement parameter is compared to a reference value.
In a further embodiment of the present invention, a diagnostic system is provided for determining a characteristic of electrode contacts and/or contacted surfaces, comprising: an RF sensor for sensing RF from partial electrical discharge events; a vibration sensor for sensing vibration from movement that causes an electrode to have a break contact event or a make contact event; circuit for determining a first time and a second time when a level of activity in the vibration signal exceeds a predetermined threshold level of activity; and a recorder for recording the RF signal and the vibration signal occurring in a time period that includes the first time and the second time.
In a yet further aspect of the invention, a circuit is included for determining a parameter of one of the RF signal and the vibration signal and comparing that parameter to a predetermined threshold.